A battery pack configured by connecting a plurality of battery cells of lithium-ion secondary batteries or secondary batteries such as nickel hydride batteries or lead batteries in a series-parallel manner is generally used together with a battery monitoring device. The battery monitoring device detects a battery state by detecting a cell voltage of each battery cell constituting the battery pack or by detecting a current flowing through the battery cell. Therefore, it is monitored whether the battery pack is in an appropriate state. In some cases, the battery monitoring device may have a function as a control device of controlling a conduction state in order to maintain the appropriate state.
In a general battery monitoring device, in order to discriminate whether or not each cell is overcharged or overdischarged, a voltage or a conducting current of each battery cell is detected or measured. In addition, in order to discriminate a deteriorated state of the battery, in some cases, an internal resistance of the battery cell may be detected. If the battery is deteriorated, the internal resistance is increased, and thus, the deteriorated state of the battery can be discriminated by detecting the internal resistance.
The detection of the internal resistance of the battery is performed by using a measured value of the voltage of the battery cell and a measured value of the conducting current. At this time, a timing of detecting the cell voltage of the battery cell by a voltage detection unit and a timing of detecting the current flowing through the battery cell by a current detection unit need to be synchronized with each other.
In a general battery state detection circuit, since the cell voltages of a plurality of the battery cells are configured to be sequentially measured, a cell voltage measurement period having a time width is needed for the measurement of the cell voltage. Therefore, it is difficult to set synchronicity between the measurement time point of the cell voltage and the measurement time point of the current to be shorter than the time width of the cell voltage measurement period. For this reason in a battery monitoring circuit of the related art, it is difficult to align the measurement time points of the voltage and the current for each battery cell, so that it is difficult to measure the internal resistance of the battery for each cell.
As a configuration of synchronizing the cell voltage detection timing and the current detection timing, considered is a configuration where a current detection unit is provided in a monitoring circuit provided with a voltage detection unit to perform detection of the cell voltage and detection of the current based on a clock of the monitoring circuit side.
However, in such a configuration, since the current needs to be detected while the cell voltage is detected for each battery cell in the monitoring circuit, there is a problem in that an amount of data treated by the monitoring circuit becomes large.
In contrast, PTL 1 discloses a configuration of allowing a deviation between the voltage detection timing in the monitoring circuit and a current detection timing in a control circuit and using a correction unit of correcting the deviation.